Slide valve for steam engines



Aug, 1-928. V

J. DOCKiNGS SL IDE VALVE FOR STEAM ENGINES Filed July 10, 1926 Invemwzr' John Dockings Patented Aug, 14, 1928.

JOHN BOOKINGS, HAMILTON, ONTARIO, CANADA.

SLIDE VALVE FOR STEAM ENGINES.

Application filed July 10,

The principal object of the invention is to effect the balancing ofslide valves for steam 'engines by reducing the area of the valveexposed to the live steam pressure and thereby reducing to a desiredminimum the friction of the valve on its seat.

The principal feature of the invention consists in the novelconstruction and arrangement of parts whereby access of the live steampressure to the major area of the back'of the valve is prevented byproviding a piston member in the back of the valve to engage a faceplate arranged parallel with the valve face, said piston member beingheld in sealing engagement with said face plate by piston means of alesser area acted on by the live steam pressure.

A further important feature consists in providing the face of thebalancing piston with a passage communicating with the exhaust passageof the cylinder thereby permitting the free escape of any steam whichmight find its way between the balancing piston and the face plate.

In the drawings Figure 1 is a mid-sectional view through the steam chestand ports of a pair of steam cylinders showing one of the valves insection; Figure 2 is a part sectional view on a reduced scale of a valveconstructed in accordance with this invention.

Certain undesirable conditions have been found to exist in the slidevalve type of steam engine since the live steam in the chest acting onthe back surfaces of the valve exerts a tremendous pressure between thevalve and its seat causing excessive wear and loss of power.

In engines where very high steam pressure is employed the conditionbecame acute and it has been found necessary to relieve the pressure onthe valve.

Various structures have been devised with a view to effecting acompensating action and thus overcome the eflects of the steam pressureonthe valve but the methods employed have not been entirely satisfactoryand were unreliable in their results.

' The present invention proposes to overcome these undesirable featuresin a simple yet highly effective and dependable manner and in carryingthe invention into effect, the valve 1 having the usual rectangularfaced portion 2' which covers and uncovers the ports to the cylinders,is provided with a 1926. Serial No. 121,628.

large shallow cylindrical bore 3 extending inwardly from the back faceof the valve.

Centrally of the shallow bore 3 and at the inner end thereofis anexternally threaded boss 4. The boss 4 is bored centrally to form acylinder '5 to receive the small piston member 6 and a passage 7 in thevalve con nects the cylinder 5 withthe steam chest. A packing nut 8 isthreaded on to the boss 1 in order torender the piston 6 steam tight inthe bore 5. V.

Slidably arranged in the cylindrical bore 3 is a shallow piston 9, rin s10 being carried thereby to effect a seal between the piston andcylinder wall and prevent the passage therebetween of live steam.

The head 11 of the piston 9 is provided with a recess 12 centrallythereof to form a narrow annular flange 13 around the periphery of thepiston head and a hole 14: through the piston head allows any steamleaking past the flange 13 to escape by way of the passages 14 in thevalve body 1 to the engine exhaust port 15, said passages 14' beingarranged either side of the central boss 4 and communicating with theexhaust port.

Extending longitudinally of the steam chest and having its flat surfacearranged in parallel relation'to the valve engaging surface of the portwall is a face plate 16.

The spacing of the plate 16 from the surface of the port wall is such asto permit of a slight clearance between the same and the back of thevalve.

The live steam pressure from the steam chest enters the passage 7 andentering the cylinder 5 exerts an outward pressure on the piston 6therein.

The outer end of the piston 6 engages the head 11 of the large piston 9and forces the piston 9 outwardly causing the annular flange 13 thereofto engage the surface of the plate 16. The engagement of the annularflange 13 of the piston with the sur face of the plate 16 effects a sealbetween the two members and consequently the effective area of the valveon which the live steam would otherwise act is reduced by an amountequal to the area of the head of the piston and as a result the pressureapplied on the valve through the action of the steam is reduced in acorresponding proportion.

Any steam which may leak past the seal afforded by the annular flange 13against the plate 16 is prevented from exerting a surface pressure onthe valve by means of the hole 14 connected with the exhaust through thepassages 14 in the valve '1.

It will be at once apparent that an arrangement such as described willbe extremely efficient in its action. The small pressure piston may bemade to any size 7 suitable for a given pressure and will ensure apositive and predetermined outward pressure on the large seahng plston 9atall times during the operation of the engine.

Oneor more piston's 6 may be used as de slred.

In single cyhnder steam engines employing only a singlevalve the plate16 will not be necessary as the balancing piston will engage the cap ofthe steam chest.

What I claim as my invention is:

A slide valve for steam engines comprising the combination with a steamchest and cylinder having inlet and exhaust ports, of

a valve body in said steam chest cooperattheendof sa'id boss and sealingsaid piston,

a passage in the valve body connecting the small cylindrical bore withthe interior of the steam chest, 7 a piston in said' sha'llowcylindrical bore having a depressed outer head and adapted to beengagedand forced outwardly by the former piston, steam pas- Sages in saidvalve-body at either side of saidcentral boss connecting theinner end ofthe shallow cylindrical "bore'with the exhaust port and a vent in thedepressed'head of the piston leading "to "the interior of the shallowcylindrical'bore. V

I JOHN DOGKTNGS.

